1. Field of the Invention
The present invention relates to a method of activating a compound semiconductor layer, necessary for manufacturing a compound semiconductor device for use in an optical device such as a blue-green light emitting device, a violet laser diode, a UV light emitting device, a laser diode or a transistor, to a p-type compound semiconductor layer.
2. Description of the Related Art
FIG. 1 is a sectional view showing the structure of a typical GaN-based optical device. As shown in FIG. 1, the GaN-based optical device is constructed such that a buffer layer 2 is formed on a sapphire substrate 1, a GaN layer 3, an n-GaN layer 4, an InGaN layer 5 and a P-type GaN layer 6 are sequentially stacked thereon, and then a p-contact layer 7 and an n-contact layer 8 are formed. The GaN optical device emits a blue, violet or green light, etc. and has a short-wavelength to provide full color display. Also, the GaN-based optical device can be applied to fields of high-capacity recording media for storing information. Also, since the GaN-based optical device exhibits excellent thermal properties, it can be applied to electronic devices capable of operating at a high temperature.
Nitride series compound semiconductors which are rapidly being developed in view of commercialization of short wavelength optical devices, entail a problem in manufacturing a p-type semiconductor, in contrast with other series materials including GaAs.
There are several well-known methods for growing a compound semiconductor layer, including a metalorganic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy method and a hydride vapor method. In a state where a GaN series compound semiconductor has a layer grown by a metalorganic chemical vapor deposition (MOCVD) method, for example, and doped with p-type impurities, the GaN layer cannot be used as a device due to its high resistivity. This is presumably because hydrogen, serving as a reaction gas during growth of the layer is bonded with p-type impurities to be contained in a crystal and thus acts to prevent the p-type impurities from being electrically activated. In order to solve this problem, there has been proposed a method of increasing electrical conductivity using an electron beam. According to this method, electron beams are irradiated into a grown layer, thereby reducing resistivity. However, this method entails the problem of the generation of defects on the surface of the layer, thus deteriorating the performance of the device. Also, since electron beams cannot be irradiated over a large surface, the irradiated electron beams, having only up to a small area where the electron beams can reach, must be sequentially scanned over the entire surface. Thus, this method is not suitable for mass production. Alternatively, there has been proposed an annealing method. According to this method, the resistivity is lowered by annealing a grown layer at a temperature of 400.degree. C. or higher. However, with this method, since the grown layer must be exposed to a high temperature of 800-900.degree. C., the surface of the layer may be damaged. Also, the impurities contained in the layer may be diffused during growth, thus deteriorating the performance of the manufactured device.